background image issue

I`ve just done my first website with HTML & CSS and was really happy that I`ve managed it so quickly (it`s simple and primitive but I do like it). Not until I opened it on another computer and I realized that it`s not finished at all....

So, I have a specific concern here, which I hope you can help me out with.

It`s about the composition of the background when opened in different resolutions

What I`ve done for the background is to safe 3 separate images:
1 image float:left
1 image float:right
1 image white gradient on top of both creating space for the conent and a smooth transitions between the two images.